In order to realize a microwave-assisted magnetic recording head, it is important to design and form a spin-torque oscillation element which can stably oscillate at low drive current. When the element size is, for example, about 70 nm, the maximum current density possible for the STO is 2×108 A/cm2. For this current density or higher, for example, heat production and migration of the spin-torque oscillator occur, thereby degrading the characteristics of the element.
When manufacturing a microwave-assisted magnetic recording head, it is necessary to align a main pole and an STO at appropriate positions. Here, a method in which the STO and main pole are processed with the same mask such in order to align the STO and the main pole in a self-aligning manner, has the following drawback. That is, when the main pole is processed by ion-beam etching (IBE), the material of the main pole reattaches to a wall on the STO side, which interferes with high-frequency oscillation from the oscillation layer. On the other hand, if the STO is formed after the main pole is formed, the reattachment of the material of the main pole can be reduced because the main pole is not formed by IBE; however other problems may arise, such as difficulty in positioning in the self-aligning manner and degraded configuration due to a remaining base portion of the STO, which causes, for example, the suppression of high-frequency oscillation and electrical contact errors. Overmilling during processing of the STO may be considered to reduce the degradation of configuration shape; however overmilling causes, as a tradeoff, promotion of reattachment of the material of the main pole. It is another alternative to consider that the wall on the STO side be protected with an oxide or the like before processing the main pole in order to prevent the reattachment of the material of the main pole. However, this alternative is not yet sufficient to further reduce the drive current of the high-frequency oscillation.